Water lily problem - brown leaves

I wonder if anyone on this group can provide some advice.

I have a newish pond - it's been filled for about two months. The
water lilies I have bought have suffered from major discolouration of
the leaves within a week or so of putting them into the pond.
Basically the leaves start going brown in patches until they are
completely brown. I can't see anything obvious like larvae. Also,
and maybe connected, the leaves are getting rather ragged at the
edges.

I'd like to understand why this is happening so that I can sort it out
before buying any more plants - they ain't cheap!

Also, the pond suffered a couple of weeks ago from very green water
but this is now starting to clear - I suspect the lousy summer weather
here in the UK has helped suppress the algae. Could this be a
contributory factor to the water lily problem?

Any ideas?